A government-issued photo ID allows a person to verify that he is who he claims to be. Although the types of ID come in different forms, many types of government-issued ID are deemed as acceptable by government entities such as the Transportation Safety Administration, police and other law enforcement officials.
Some of the forms of government-issued ID that the TSA accepts include U.S. passports, drivers licenses issued by a state's Department of Motor Vehicles, U.S. military ID, permanent resident cards, and foreign government-issued passports.
A government-issued ID is often requested or needed to ensure physical and financial security. For example, a person who wants to fly must produce identification. Likewise, a person who wants to take a car loan or a home loan from a bank must be able to prove that he is who he says he is. In some instances, a government-issued ID is needed to vote, though making this a requirement is often debated.
In some instances, the government has other ways of verifying identities when an ID is lost or forgotten. For example, the TSA is sometimes able to use databases to verify the identities of those who arrive at an airport without their proper ID.